This invention relates to a process for preparing rhodium(I) carbonyltriorganophosphorus mono-.beta.-ketoenolate complexes from halocarbonylbis(triorganophosphorus) rhodium(I) complexes. Such complexes are useful as catalysts in hydroformylation processes. Hydroformylation is the general term applied to the reaction of an olefin with hydrogen and carbon monoxide to form an aldehyde.
U.S. Pat. No. 3,527,809 (Pruett, et al.) discloses an improved rhodium-catalyzed hydroformylation process which results in a high ratio of normal to branched-chain aldehydes. This process has proven very successful commercially. In this process certain rhodium complexes (i.e. catalyst precursors) are added to the reaction medium. For example, acetylacetonatodicarbonyl rhodium(I) (Rh(CO).sub.2 acac) can be added to the reaction medium where it forms active catalyst. Another such catalyst precursor is acetylacetonatocarbonyl(triphenylphosphine) rhodium(I) complex (hereinafter referred to as "Complex I"). The basic hydroformylation process of Pruett, et al. has been further improved since its invention. Such further improvements include removing product aldehyde by recycling gas (U.S. Pat. No. 4,247,486), providing an alkyldiaryl phosphine ligand in the reaction medium (U.S. Pat. No. 4,260,828) and using the rhodium catalyst in a condensate solvent (U.S. Pat. No. 4,148,830).
It is known that the rhodium complex catalyst loses activity (i.e., becomes partially deactivated) during prolonged use in such hydroformylation processes. Because of the high cost of rhodium, several methods have been developed to maintain the level of activity of the catalyst and to reactivate deactivated catalyst.
U.S. patent application Ser. No. 120,101 filed Feb. 28, 1980, now U.S. Pat. No. 4,297,239 discloses a method of concentrating the spent hydroformylation reaction medium using a distillation technique in a wiped film evaporator. The resulting rhodium complex concentrate, especially when supplemented with a treatment by air, is an active catalyst precursor.
The rhodium complex concentrate may alternatively be treated according to the method disclosed in U.S. patent application Ser. No. 221,502, filed Dec. 30, 1980, now U.S. Pat. No. 4,363,764. This process entails treating the distilled rhodium complex concentrate with a halide ion source, a carbon monoxide source and free triorganophosphorus ligand, initially to prepare a halocarbonylbis(triorganophosphorus) rhodium(I) complex ("Complex II"). Ser. No. 221,502 further discloses that if Complex II is reacted with a metal hydride reducing agent and free triorganophosphorus ligand without isolating Complex II from its product mixture, the reaction process will form a hydridocarbonyltris(triorganophosphorus) rhodium(I) complex, which is useful as a hydroformylation catalyst precursor. Although Ser. No. 221,502 broadly discloses that Complex II is useful as source material for catalyst precursors, no process for producing a .beta.-ketoenolate rhodium complex precursor is disclosed.
U.S. Pat. No. 4,021,463 discloses a process for preparing Complex II by treating the distillation residue of a hydroformylation mixture with an aqueous mineral acid and a peroxide to convert the rhodium into a water-soluble salt which passes into the aqueous phase, mixing the resulting aqueous salt solution with a solvent, tertiary phosphine and hydrohalic acid or metal halide and reacting the aqueous solution with carbon monoxide or a carbon monoxide donor. Said patent further discloses that the hydridocarbonyltris(triorganophosphine) rhodium(I) complex, an active catalyst precursor, can be produced by simultaneously subjecting the aqueous starting solution to hydrogenation conditions or by subjecting a solvent solution of the halo-containing compound together with additional phosphine to hydrogenation conditions.
U.S. Pat. No. 4,113,754 discloses a process for preparing chlorocarbonylbis(triorganophosphine) rhodium(I) complexes ("Complex IIA") by treating a distillation residue of a hydroformylation mixture with oxygen-containing mineral acids and peroxides to form an aqueous rhodium salt solution which is then treated with a cation exchanger. The complexed rhodium ions are then eluted with hydrochloric acid and the solution obtained is reacted in the presence of a water-soluble organic solvent, a tertiary phosphine and carbon monoxide to produce Complex IIA. The patent further discloses that if the latter reaction is carried out under hydrogenation conditions, hydridocarbonyltris(triorganophosphine) rhodium(I) is produced.
Various processes are known for producing rhodium(I) carbonyltriorganophosphorus mono-.beta.-ketoenolate complexes. By way of illustration, "Dicarbonyl-.beta.-diketonato and Related Complexes of Rhodium(I)," Bonati and Wilkinson, J. Chem. Soc. 3156 (1964), discloses a process involving the following reactions: EQU RhCl.sub.3 +CO.fwdarw.[Rh(CO).sub.2 Cl].sub.2 ( 1) EQU [Rh(CO).sub.2 Cl].sub.2 +CH.sub.3 COCH.sub.2 COCH.sub.3 +BaCO.sub.3 .fwdarw.Rh(CO).sub.2 acac(acac=CH.sub.3 COCHCOCH.sub.3.sup.-) (2) EQU Rh(CO).sub.2 acac+Ph.sub.3 P.fwdarw.RhCO(Ph.sub.3 P)(acac)(Complex I) (3)
Japanese Pat. No. 75/53293 also discloses above Reaction (3). In addition, "Preparation and Reactivity of Some Halogen Bridged Complexes of Rhodium(I)," Barlex, Hacker and Kemmitt, J. of Organometallic Chemistry, 43 (1972) 425, discloses the following reaction for the preparation of Complex I: EQU Rh(PPh.sub.3).sub.2 acac+CO.fwdarw.RhCO(PPh.sub.3)(acac)+PPh.sub.3 ( 4)
It also discloses the facile conversion of Complex I and analogous compounds to halocarbonyl(triorganophosphine) rhodium(I) complexes by reacting them with hydrogen halides.
Thus the prior art does not disclose a process for producing any rhodium(I) carbonyltriorganophosphorus mono-.beta.-ketoenolate complex (e.g., Complex I) directly from a halocarbonylbis(triorganophosphorus) rhodium(I) complex (Complex II). The preparation of Complex I from RhCOCl(PPh.sub.3).sub.2 can be represented hypothetically by Reaction (5) (displacement of chloride and triphenylphosphine from RhCOCl(PPh.sub.3).sub.2 by acetylacetonate anion): EQU RhCOCl(PPh.sub.3).sub.2 +acac.sup.- .fwdarw.RhCO(PPh.sub.3)(acac)+Cl.sup.- +PPh.sub.3 ( 5)
However, while displacement reactions of coordinated chloride for the preparation of certain metal acetylacetonato derivatives are well known and are described in the prior art (see "Metal .beta.-Diketonates and Allied Derivatives," Mehrota, et al., Academic Press, 1978, 18), it has now been found that Reaction (5) does not proceed or proceeds sluggishly to low conversions of Complex I (see Example 2 below). In fact, not only is RhCOCl(PPh.sub.3).sub.2 a poor substrate for displacement of chloride by acetylacetonate anion, but it is well known that, with only a few exceptions, anionic displacement of chloride from RhCOCl(PPh.sub.3).sub.2 proceeds poorly, if at all. Following known procedures for preparing anionic displacement products of RhCOCl(PPh.sub.3).sub.2, the latter is first converted into RhCOF(PPh.sub.3).sub.2 or RhCO(ClO.sub.4)(PPh.sub.3).sub.2 [see "Fluoro Complexes of Rhodium(I) and Iridium(I)," Vaska and Peone, in Inorganic Syntheses, Parshall, editor, McGraw-Hill, 1974].
Various methods are known for oxidizing tertiary phosphines existing in free as well as coordinated states. However, there is no known method for preparing a rhodium(I) .beta.-ketoenolate complex whereby the prior or simultaneous oxidation of a coordinated tertiary phosphine facilitates the substitution of a coordinated halide by .beta.-ketoenolate to form said .beta.-ketoenolate complex. The various known methods for oxidizing tertiary phosphines (free and coordinated) are illustrated by the following references.
"Tertiary Phosphine Oxides" (Hays and Peterson), which appears as Chapter 6 in Organic Phosphorus Compounds, Vol. 3 (Kosolapoff and Maier) discloses a method of oxidizing free tertiary phosphines to make phosphine oxides using a variety of oxidizing agents, including oxygen, peroxy compounds, olefin epoxides, nitrogen oxides, sulfur oxides and standard inorganic oxidants. Hays et al. also specifically discloses the use of t-butyl hydroperoxide for oxidizing free tertiary phosphines.
A literature and patent survey entitled "Tertiary Phosphines as Catalysts" (M. K. Moran, M & T Chemicals, Inc., 1975) discloses methods of oxidizing free trialkylphosphines using nitric acid, aqueous potassium permanganate, hydrogen peroxide, ferric chloride, olefin epoxides, and cyclic carbonates to produce trialkylphosphine oxides.
"In situ High Pressure, High-temperature Spectrophotometric Studies of the Chlorocarbonylbis(triphenylphosphine)rhodium(I) Hydroformylation Catalyst Activated by Hydroperoxides," Tinker and Morris, J. Organometallic Chem. 52, 1973, C55, teaches, among other things, that in the presence of one equivalent of an organic hydroperoxide (cyclohexenyl hydroperoxide) and under hydroformylation conditions, RhCOCl(PPh.sub.3).sub.2 is converted into cis-Rh(CO).sub.2 ClPPH.sub.3 : ##STR1## This is a substitution process of Complex (IIA) facilitated by oxygen transfer where the neutral triphenylphosphine ligand undergoing substitution (and oxidation) is being substituted by another neutral ligand, CO. It is not obvious from this, however, that in the presence of an oxygen transfer agent and an anionic ligand that substitution of the chloride in Complex (IIA) will occur to yield Complex (I): EQU RhCOCl(PPh.sub.3).sub.2 +acac.sup.- +RO.sub.2 H.fwdarw.RhCO(PPh.sub.3)acac+Ph.sub.3 PO (Complex I)
Trimethylamine N-oxide has been employed extensively and exclusively to promote the substitution of coordinated CO in metal carbonyls by other neutral ligands including tertiary phosphines via prior or simultaneous oxidation of the coordinated CO (Blumer, Barnett, and Brown, J. Organometallic Chem., 173, (1979), 71-76, and references cited therein). However, none of these references discloses or suggests the use of trimethylamine N-oxide in the context of the present invention, namely, promoting substitution of a coordinated anion in a metal carbonyl by first or simultaneously oxidizing a coordinated tertiary phosphine ligand.
Thus, it is an object of this invention to provide a process for preparing rhodium(I) carbonyltriorganophosphorus mono-.beta.-ketoenolate complexes from halocarbonylbis(triorganophosphorus) rhodium(I) complexes.
It is a further object of this invention to provide a process for preparing hydroformylation catalyst precursors.
It is still a further object of this invention to convert halocarbonylbis(triorganophosphorus) rhodium(I) complexes directly to rhodium(I) carbonyltriorganophosphorus mono-.beta.-ketoenolate complexes.